There is great interest in the high temperature superconductor (HTS) coated conductor community to develop economically scalable processes for fabricating bi-axially textured templates on which high quality YBa2Cu3O7-Δ(YBCO) can be heteroepitaxially deposited. In order to achieve good superconducting properties, YBCO grains require good alignment between each other to obtain high (>1 MA/cm2) critical current densities (Jc). The two competitive processes to produce the bi-axial texture required by YBCO have been Roll-Assisted BI-axial Texturing of Substrates (RABITS) and Ion-Beam Assisted Deposition (IBAD).
The latter technique has been used in the development of IBAD deposited yttria-stabilized zirconia (YSZ) for coating meaningful lengths on commercially important metal substrates. Further efforts have resulted in development of a process, coupled with pulsed laser deposition (PLD) YBCO, that has produced meter lengths of superconducting wire with critical current densities over 1 MA/cm2 and critical currents over 100 A. Despite these results, one criticism of the IBAD-YSZ process has been that the time required to deposit the material with sufficient in-plane texture for high quality YBCO is too long. In order to develop texture, YSZ requires a thickness of between 0.5 and 1 micrometer (μm) to achieve a Δφ (or full width at half maximum of the φ-scan peak) better than 12°. Reported IBAD deposition times have ranged from about one to twelve hours per meter of tape. Thus, the viability of this process has been questionable for cost efficient, industrial fabrication.
Subsequently, it has been shown that magnesium oxide (MgO) can be deposited with the IBAD process and produce a thin film with in-plane texture comparable to YSZ that was only 10 nanometers (nm) thick. This translates to a process about 100 times faster than IBAD YSZ. This process has been applied to further development in the preparation of FITS coated conductors. For example, short length samples (less than about 4 cm long) using IBAD MgO templates have been produced with Jcs over 1 MA/cm2 (77 K) for>1.5 μm thick YBCO films.
However, IBAD MgO still has some drawbacks that detract from its viability as a template layer for long length processing of coated conductors. The two most detrimental limitations are (1) the degradation of in-plane texture as IBAD MgO film thickness increases beyond a critical thickness of 10 nm; and, (2) the necessity to deposit IBAD MgO films on very smooth (<2 nm rms) substrates.
Dong et al., Journal of Materials Research, vol. 16, pp. 210-216 (2001), have suggested a dual ion beam approach for control of texture in aluminum films, but contain no hint of the applicability to the deposition of MgO films for the subsequent deposition of thin films such as YBCO.
After extensive and careful investigation, the present inventors have now developed an IBAD deposition process using dual ion beams in deposition of intermediate layers for the subsequent deposition of thin films such as YBCO.